Delrin CNC machining is one of the most common requests in plastics work, and for good reason. Acetal, also called polyoxymethylene or POM, is stiff, low friction, dimensionally steady and easy to cut to close sizes. Delrin is the familiar homopolymer brand; acetal copolymer is sold under several names and trades a little strength for better chemical resistance and less centerline porosity. Wexmar machines both grades on CNC lathes, Swiss-type machines and horizontal machining centers at our shop in Canastota, New York, from single prototypes through production runs.
Machinability of acetal
Plastics are not rated on the AISI 1212 steel scale. Acetal cuts freely and gives some of the cleanest chips of any engineering plastic, so machine time is rarely the limiting factor. The real limits are heat, internal stress, clamping pressure and dimensional stability. Acetal expands with heat far more than metals do, so a part measured warm off the machine can read differently an hour later. We rough, let parts rest, then take finish passes, and we inspect at shop temperature.
Tolerances and surface finish
For precision Delrin turned parts, plus or minus 0.001 in. is typical on small diameters and bores, and plus or minus 0.002 in. on larger turned and milled features. Larger parts and thin walls are reviewed individually, since stress and temperature affect them more. A 32 Ra finish is typical on turned bearing surfaces, and 63 Ra on milled faces. Acetal takes a clean, slightly glossy finish straight from a sharp tool with no polishing required.
Tooling, heat and chip control
- Sharp, polished tools. Uncoated or polished carbide with high positive rake and generous clearance keeps the cut clean. Tools used on metal are kept separate, because a slightly dull edge rubs and melts the surface.
- Heat management. Air blast or water-soluble coolant carries heat away. Too much heat causes smeared finishes, gummy burrs and dimensional drift.
- Stringy chips. Acetal can produce long continuous ribbons on the lathe. Chip-breaking inserts and interrupted feed cycles keep them from wrapping the part.
- Centerline porosity. Thick homopolymer rod can have porosity at the center. For pressure-holding or fluid parts, copolymer or a porosity-free grade is often the better choice.
- Clamping. Soft jaws, light pressure and full-contact fixtures prevent distortion that springs back once the part is released.
- Burrs. Burrs are light and fuzzy and are removed with a blade or by programmed edge breaks.
Stress relief and finishing
For tight-tolerance or thin-wall acetal parts, annealing the stock or the roughed part relieves internal stress and reduces movement after machining. Annealing is performed through qualified outside processors, or by specifying stress-relieved stock from the mill. Most acetal parts ship in the as-machined condition. Secondary finishing such as printing or marking, when needed, is arranged through qualified outside processors.
Common Delrin and acetal parts
- Gears, sprockets and cams (horizontal mills, lathes with live tooling)
- Bushings, bearings and thrust washers (CNC lathes)
- Rollers, guides and wear pads for conveyors and packaging lines (lathes and horizontals)
- Valve seats, poppets and manifold blocks for fluid handling (lathes and horizontal milling)
- Small insulators, spacers and connector components (Swiss-type, parts to 32 mm diameter)
- Fixture pads and soft locators for assembly and inspection
Small diameter acetal parts in volume run well on our Swiss machining cells with bar feeders. Larger blocks and gear blanks run on our CNC turning lathes and horizontal mills.
Cost index vs 6061 aluminum
| Material | Approx. machinability (1212 = 100) | Cost index vs 6061 | Notes |
|---|---|---|---|
| 6061-T6 aluminum | ~180 | 1.0 | Baseline |
| Delrin / acetal | Not rated; cuts freely | 1.0 | Stiff, low friction, stable |
| Nylon 6/6 | Not rated; cuts freely | 1.0 | Tougher, absorbs moisture |
| UHMW | Not rated; cuts freely | 1.1 | Wear strips, low precision |
| Polycarbonate | Not rated; cuts freely | 1.3 | Clear, impact resistant |
| PTFE | Not rated; cuts freely | 1.4 | Lowest friction, creeps |
| PEEK | Not rated; cuts freely | 4.5 | High heat and chemical resistance |
These values are typical and illustrative for a comparable part; actual quotes depend on geometry, quantity, tolerances and mill pricing. When a part sees moisture and impact more than precision, compare acetal with nylon 6/6 machining.
Applications and industries
Acetal CNC machining services support industrial OEMs in power transmission, packaging and conveying, fluid power and pumps, electrical and connector assemblies, instrumentation, and medical hardware such as instrument handles and fixture components. For food-contact parts, FDA-compliant acetal grades are available from the mill with documentation. Customers in Central New York and across the country receive parts by LTL or parcel from Canastota.
Getting a quote
To price Delrin or acetal parts, upload a drawing for an instant estimate or call (315) 400-2654. A human estimator confirms every quote, including the grade, color and stock size needed.